Double acting two stroke cycle internal combustion engines



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A. DOUBLE ACT INTERNAL AZVIZW 4 MfaA/h 3 www sept. 21, 1965 Filed Feb.24, 1964 A. E. BROWN DOUBLE ACTING TWO STROKE CYCLE Sept. 21, 1965INTERNAL COMBUSTION ENGINES Filed Feb. 24. 1964 9 w w 4 M l f 7 //V w/ IH. lan I u s 5 5 2 O u 5 O l 7 I O O :4J IIH 6 nl .l O I 6| I I I f/ONMM@ H 6 1 al [Iwl I 12% Il vvf/ H/ \1\\\\\\\ J 4 u I fm w/ V 6 l m H OJO M I u /O O I 6 I II //O 4 H 2 I l 7 Isl H II l Imi Ia I 5% \k n\\ 7 f9 I|| I LII 5 E /lwml/ I d .Ur V 4 m n ,4, 4

Sept. 21, 1965 A. E. BROWN DOUBLE ACTING TWO STROKE CYCLE INTERNALCOMBUSTION ENGINES 5 Sheets-Sheet 3 Fled Feb. 24, 1964 United StatesPatent O 3,207,139 DOUBLE ACTING TWO STROKE CYCLE INTER- NAL COMBUSTIONENGINES Arthur E. Brown, 118 W. 6th St., Corning, N.Y. Filed Feb. 24,1964, Ser. No. 346,964 Claims. (Cl. 123-57) This invention relates todouble acting two stroke cycle internal combustion engines.

In the past, commercial manufacture of double acting two stroke cycleengines has been mostly limited to the large slow turning engines ofseveral thousand HP.; and these engines have individually fabricateddouble acting cylinders, with individual heads on each end, all boltedto a lower frame structure which includes cross head guides. These priorengines are further characterized in that -a conventional cross head,piston rod, and stufling box is employed with each double acting piston.The cylinder generally contains in the walls intermediate its lengthboth inlet and exhaust ports.

A main object of this invention is to provide a double acting engine inwhich the crankcase and cylinder block structure is formed as anintegral casting similar to present day automotive single actingengines.

In single acting engines, the advantages of making the crankcase andcylinders a single cast structure is well known. These advantages are:(1) a lighter weight but more rigid structure, (2) more compact throughelimination of flanged joints, (3) lower cost automat-ic machining ofparallel cylinder bores in a transfer type machine, (4) less assemblycost, (5) fewer parts, and (6) better control of machining tolerances.This invention now secures the above six advantages in a double actingtwo stroke cycle engine.

Another object is to provide a double acting engine in which thecylinder bores can be machined from the top of the 'cylinder block witha boring oper-ation similar to present single acting engines and inwhich each cylinder bore serves a double acting piston assembly.

Another object is to provide .an improved reciprocating rod and rod sealconstruction for the embodiment shown in FIGS. I, II, and III.

An advantage of this invention is that the problem of misalignmentbetween the front and back working cylinders (or liners) is eliminated.Concentricity is assured because of through boring of the cylinder blockand elimination of `bolted joints.

Another object is to provide a double acting engine that is economicalto manufacture. This objective is achieved rst, because the usual crossheads and cross head guides are not required; and second, because thecylinders and crankcase are formed as an integral casting and thecylinders bored in a manner similar to present single acting automotiveengines all without the need of a bolted joint for the cylinders to thecrankcase or a bolted joint intermediate the cylinder length.

An advantage is that the cylinders can be closely spaced in amulticylinder in line engine. This is made possible through theelimination .of bolted joints in cylinders and crankcase.

Another object is to provide a double acting engine (without cross headsor cross head guides) in which the pistons can be removed withoutremoving the crankshaft and in which all the pistons may be installedfrom the top and so that the main bearings need not be made small enoughto clear the pistons.

An object is to provide removable and replaceable cylinder liners andseals `for wet type liners.

Another object is to provide a confined gasket seal between the cylinderliners and the inserted head for sealing in combustion gas.

Another object is to provide a simple and etective ICC method ofconducting liquid coolant from the cast cylinder block to an insertedcylinder head.

The engines described in this application and in my copendingapplication (Serial No. 209,619, filed July 13, 1962, now Patent No.3,159,147) have the following seven common advantages:

(l) The engine has two power strokes per rotation of each crank andconnecting rod. Therefore, the two crank engine shown in FIG. IV canprovide the same number O of power impulses as an eight cylinderfour-stroke single acting engine.

(2) The engine is able to operate at high speed without subjecting theconnecting rod and bearings to high reciprocating inertia forces becausethe inertia forces are opposed at the end of each stroke by a gaspressure force.

(3) The load -on the piston pin bearing is bi-directional (instead ofunidirectional as in single acting two-stroke engines) and the loadreversal aids its lubrication process.

(4) In the embodiment shown in FIGS. IV and V, the engines have unillowtype scavenging. This means the iiow of scavenging air (or fuel-airmixture) through each working chamber is more orderly in character withless mixing, less sholt circuiting, and less eddy currents than areassociated with cross ow or loop scavenging.

(5) In the embodiment shown in FIGS. IV and V, the engine has inherentfree breathing, faster running characteristics made possible by unillowscavenging which provides large port areas with minimum port height.

(6) The pistons remain cooler since each working piston (in an assembly)is exposed to combustion on one end only. Also, in FIGS. IV and V theflow of scavenging air through the pistons aids the cooling process.

(7) The engines are compact and light in weight because: (a) they aredouble acting without need Vof a cross head, (b) they are well suited tooperate at high speed, and (c) in the FIGS. IV and V embodiments theyhave a high B.M.E.P. because of uniow scavenging and short port height.

These and other objects and advantages will be more apparent from thedrawings and description.

Throughout the description and claims, the front of the engine is nearerthe crankshaft than the back.

FIG. I is a sectional view of a cross flow scavenged double actingengine.

FIG. II is an enlarged partial section view of the engine shown in FIG.I and illustrates the rod seal parts when at top dead center.

FIG. III is the same as FIG. II except the parts are shown at the bottomdead center position.

FIG. IV is a sectional view of a two crank double acting uniflowscavenged engine. The section is taken through the axi of the cylindersand the crankshaft.

FIG. V is a sectional view of a double acting uniflow scavenged engine.This engine is self scavenged without the need of a separate scavengepump.

Referring to FIGS. I, II, and II, the crankshaft 1 is rotatably mountedin the crankcase 2, the upper half of which is cast integral with thecylinder structure 3. A long cylindrical bore 4 is machined in thecylinder structure, Into this bore is stacked a front cylinder liner 5,head gaskets 6 and 6, inserted cylinder head 7, and an identical backcylinder liner 8. This stacked assembly of parts is held tightly inplace by the valve plate 9 and inlet casting 10.

A spark plug 11 is shown serving the front combustion chamber 12. Asimilar plug (in another section plane) serves the back combustionchamber 13.

Operation -of the engine shown in FIG. I is as follows: Upward motion ofthe pistons draws air (or a fuel-air mixture) through the reed valve 14.Downward motion partially compresses the air in the crankcase and nearbottom dead center the air passes through the by-pass 15, through inletports 16, and -scavenges the front working chamber 12 with a c-ounterowscavenging action exhausting through exhaust ports 17 which areuncovered by the front piston 18. A subsequent compression and powerstroke then occurs.

Downward motion of the pistons draws air through the reed valve 19 intochamber 20. Upward motion partially compresses the air in chamber 20until at near top dead center, the air flows through the by-pass 21,through inlet ports 22, and scavenges the back working chamber 13 with acounterflow scavenging action exhausting through exhaust ports 23 whichare uncovered by the back piston 24. Y

The method of sealing the reciprocating rod 25 is a critical itembecause there is a two cycle combustion chamber on each side of thecylinder head 7 and hence a double heating effect and a double sealingrequirement. Sealing is accomplished by providing each working piston 18and 24 with an integral hollow sleeve 26 and 27 each of which carries anexpanding type seal ring 28 located in a ring groove machined in theouter end of each sleeve. The expanding type Seal rings 28 press outagainst and seal against the central bore 29 in the cylinder head 7 andthus prevent leakage of gas from one combustion chamber to the other.The length of the bore in the cylinder head is suciently long that therings 28 never withdraw from the bore during their reciprocative strokeand are thereby retained in their grooves.

The sleeves also perform a shielding function in addition to theirsealing function. That is, they surround the rod 25 and thus shield itfrom high temperature combustion gas.

The preferred combination is to make the pistons and their sleeves 26and 27 of aluminum alloy and the rod 25 of high strength steel.

The function of the rod 25 and clevis 30 is to transmit the drivingforce of the back piston 24 to the piston pin 31 and the rod is made assmall in diameter as practicable in order to keep down its reciprocatingweight and also to permit the outer diameter of the sleeves to be small.With a small diameter rod, the tensile stress in the rod is high but byshielding the rod with the sleeves as described, the rod is keptrelatively cool and its strength in service is retained.

The aluminum sleeves 26 and 27 are not called upon to transmit the forceof combustion and hence high tensile strength for the sleeves is not arequirement. The function of the sleeves is only to shield the rod andcarry the seal rings 28. By making the sleeves and the pistons of analuminum alloy there is the two fold advantage of less reciprocatingweight and better conduction of heat away from the sleeves into thepistons where the heat is then dissipated through the cylinder walls tothe coolant. It is noted that the two sleeves are separated by a gap 32so as .n

to allow for thermal expansion. The sleeves are heated to a highertemperature than the rod and (being made of aluminum) have a highercoefficient of expansion than the steel rod and hence expand more thanthe rod. The thermal expansion does no harm since each end of the sleeveis free to lengthen within the bore 29.

The sleeves with their seal rings function in a unique and unexpectedway next described. The seal rings alternately move away from eachcombustion chamber at the time of peak pressure and peak temperature,ie., when the front piston 18 is at top dead center as shown in FIG. II,the pressure and temperature in the front combustion chamber 12 is atits peak; and at the same moment, the seal rings 28 have moved to thetop position in their bore so that they are farther away (distance A inFIG. Il) from the flame, pressure, and temperature in the frontcombustion cham-ber 12. This means that Vthe aluminum sleeve 26 servesas a buffer seal for the rings and thus protects the rings from hightemperature combustion gas which must travel distance A along thelclearance space 33 bore reaching the seal rings 28. The gas will be ata much lower temperature and slightly lower pressure when it reaches theseal rings lsince it is cooled and throttled in the narrow clearancespace 33 between the sleeve 26 and the water jacketed bore 29 in thecylinder head.

It is well known that overheating (a major cause of ring failure in acombustion engine) causes the lube oil in the ring grooves to coke upand stick the rings.

Alternatively when the back piston 24 is at bottom dead center, theflame, pressure, and temperature in the back combustion cham-ber 13 isat its peak, but the seal rings are again protected by virtue of thefact that they are at the opposite end -of the bore in the cylinder head(at a distance B in FIG. III). This unique but simple `action solves adiiiicult sealing problem Where in a double acting two stroke cycleengine, heat on the `sealing elements is otherwise lsevere because ofthe double heat ow.

It is noted that the outer diameter C of the sleeve 26 is made with aclose running clearance within the cylinder head bore 29 so as to retainthe advantage of the buffer seal effect described in the precedingparagraph.

The passages 34 are for liquid coolant. An annular coolant chamber 35 isprovided in the inserted cylinder head. A drilled hole 36 conducts thecoolant from passage 34 into the chamber 35. An elastomeric ring 37surrounds the hole and prevents leakage, The ring 37 fits in a groovemachined on the outer diameter of the inserted cylinder head 7. Thegroove does not surround the head 7 but merely extends locally aroundthe hole 36. The plug 38 seals up the outer end of the hole. Coolantleaves chamber 15 through a `similar hole not shown. yCooling of theinserted head is important since it has a two stroke cycle combustionchamber on each end of it and is depended upon to aid the coolingprocess of the sleeves 26 and 27.

The rod 25 is fastened to the back piston by means of the hollow steelcone 3.

Referring to FIG. IV, the crankshaft 40 is mounted in the crankcase 41to which is integrally cast a cylinder structure 42. The cylinderstructure has two parallel cylinder bores 43. Into each bore is stackeda front cylinder liner 44, an identical back cylinder liner 45, aninserted cylinder head 46, and soft metal head gaskets 47. This stackedassembly of parts is held tightly in place by the inlet manifold 48. Theinserted common cylinder heads are thus supported in axial positionwithin the cylinder bores by means of direct compression loading of thecylinder liners.

The FIG. IV engine requires a minimum of four spark plugs, at least onefor each combustion chamber. It is noted that the spark plug 49 threadsinto and seats directly against the inserted head 46 through a clearancehole 50 in the side of the cylinder structure.

Liquid coolant is conducted into and out of the annular chambers 51 inthe same manner as was described for FIG. I.

Operation of the engine shown in FIG. IV is as follows: Scavenge air (ora fuel-air mixture) is supplied through the inlet manifold from ascavenge pump (not shown) to the chambers 52. The scavenge air thenflows through the perforated cones 53 into the interior of the backvalve pistons 54. The front and back valve pistons 55 and 54 areseparated by annular gaps 56. Near bottom dead center, the front valvepistons 55 uncover the front inlet ports 57 (which are in the form ofslots in the cylinder head) and the front working pistons 58 uncover theeX- hauSt ports 59 in the front liners 44 so that the front workingchambers 60 are vscavenged with a uniow type Vscavenging operation. Neardead center, the annular gaps 56 overlap the back inlet ports 61 and theback pistons 62 uncover the exhaust ports 63 formed in the back cylinderliners 45 so that the back working chambers 64 are scavenged with auniflow type scavenging-operation.

The cast in passages 65 and 66 serve as collectors or manifolds for theexhaust gas.

It is pointed out that the cylinder liners in each embodiment are uniquein that they perform four functions simultaneously and these are; (1)The liners can be made of a special grade of cast iron (differing fromthat of the cylinder block) and therefore provide a hard long wearingsurface, (2) if and when the liners wear out, they can be replacedwithout replacing the whole cylinder block, (3) the liners provide aconvenient way of forming the exhaust ports by machining the ports inthe wall of the liner, and (4) the liners now serve as a very convenientmethod of supporting the inserted cylinder head.

The liners also provide a convenient method of capturing the soft metalseals 47 or 6 in a confined space. That is, the seals are confined onall Sides so that they cannot flow out of their sealing position under ahigh clamping pressure.

The front and back pistons 58 and 62 are interconnected by means of thetension rods 67 and perforated cones 53. Conventional connecting rods 68and piston pins 69 are provided.

The cylinder liners 44 and 45 are of the dry type.

Referring to FIG. V, the engine is provided with a disk 70 attached tothe rod 71 so that the crankcase 72 and back pump chamber 73 can serveas scavenge pumps las the disk 70 prevents alternate flow of fuel airmixture from one chamber to the other during pumping. y The operation ofthe engine shown in FIG. V is as follows: Upward motion of the pistonsdraws air (or a fuel air mixture from a carburetor not shown) throughthe reed valve 74 into the interior of the crankcase. Downward motion ofthe pistons partially compresses the fuel air mixture in the crankcaseso that when the pistons near bottom dead center, the precompressedmixture flows up through the hollow front valve piston 7S, through theannular gap 76, through the front inlet ports 77, and scavenges thefront working chamber 78 with a uniow scavenging operation exhaustingthrough exhaust ports 79. Upward motion of the pistons compresses thecharge in the front working chamber where it is ignited by means ofspark plug 80 and a subsequent power stroke occurs.

Similarly, downward motion of the pistons draws a fuel air mixturethrough the reed valve 81 into the back pump chamber 73. Upward motion`of the pistons partially compresses the mixture in the chamber 73 andnear top dead center the back valve piston 82 begins to uncover the backinlet ports 83 so that the fuel air mixture ows through the back valvepiston 82, through the annular gap 84, through the back inlet ports 83,and scavenges the back power chamber 85 with a uniow scavengingoperation exhausting at the exhaust ports 86 which are uncovered by theback working piston 87. Downward motion of the pistons compresses andthen fires the mixture in the back power chamber 85 from a spark plugnot shown.

The cylinder liners 88 are 4of the wet type along a portion of theirlengths. The water passages 89 surround the liners and the cooling waterows directly against the cylinder liners. Elastomeric O rings 90 and 91lit in internal grooves machined in the Walls of the cylinder bore andprevent leakage of the coolant. The O rings are installed without beingcut -by sharp metal edges (during liner installation) because the bottomedges 92 and 93 of the cylinder liners are chamfered and the edges ofthe ports 79 and 86 are rounded and polished.` Locating the O rings inthe cylinderstructure (instead of the liners) keeps the O rings cooler.

The long spark plug 80 threads into and seats against the insertedcylinder head 94 and is also sealed at 95 to prevent coolant leakage.

The exhaust manifolds or collectors 96 are fastened to the cylinderstructure.

A feature of the FIG. V engine is that the liners (being of the wettype) are easier to remove and this is an advantage since it permitsremoval of the front piston without removing the crankshaft.

In FIGS. I, IV, and V, a front cylinder liner 5, 44, or 88 is shown forsupporting the inserted cylinder head. An alternative but less preferredconstruction would vbe to let the inserted head 7, 46, or 94 restagainst a step in .the cylin-derblock bore instead of against a frontliner. This alternative construction still employs the back cylinderliner 8, 45, or 88 in each case for retaining the inserted cylinderhead.

The engine shown in FIGS. I and V can also be made multi-crank with anin line cylinder arrangement similar to FIG. 1v,I

While the preferred embodiments of the invention have been described, itwill be understood that the invention is not limited thereto since itmay be otherwise embodied within the scope of the following claims.

What is claimed is:

1. 1n a double acting two stroke cycle internal combustion engine, thecombination of a crankcase, a crankshaft rotatably mounted in saidcrankcase, a cylinder structure fastened to said crankcase, saidcylinder structure having within it a front Working cylinder and a backworking cylinder, a cylinder head inserted into the cylinder structureand located between said front and back working cylinders, said frontand back working cylinders having respective front and back combustionchambers within them, said back working cylinder having within it acylinder liner, a front working piston reciprocable in said frontworking cylinder, a back Working piston reciprocable in said liner inthe back working cylinder, said cylinder head having a central bore,`said pistons being mechanically interconnected through said bore in thecylinder head so as to reciprocate in unison, a connecting rod forconverting the reciprocating motion of said pistons to the rotary motionof said crankshaft, said liner having exhaust ports in its wallcontrolled by said back piston, said liner also serving to retain saidcommon cylinder head in axial position within said cylinder structure,said engine being adapted to be cooled with a liquid coolant, saidcylinder structure and said cylinder head having passages for the ow ofsaid liquid coolant, passage means for conducting the ow of said liquidcoolant into said cylinder head, an ignition plug for each of saidcombustion chambers, and each ignition plug being in ring communicationwith its respective combustion chamber.

2. In a double acting two stroke cycle internal combustion engine, thecombination of a crankcase, a crankshaft rotatably mounted in saidcrankcase, a cylinder structure, said cylinder structure and at leastpart of said crankcase being an integral casting, said cylinderstructure having at least one cylinder bore, a cylinder head inserted insaid cylinder bore so as to divide the cylinder bore into a frontworking cylinder and a back working cylinder, a front working pistonanda back working piston reciprocable in their respective workingcylinders, said cylinder head having a central bore smaller in diameterthan either of said working pistons, said two working pistons beingmechanically interconnected through said bore in the cylinder head so asto reciprocate in unison, a connecting rod for converting thereciprocating motion of said pistons Vto the rotary motion of saidcrankshaft, retaining means for retaining said cylinder head in axialposition within said cylinder bore, said retaining means being ofsuflicient strength to resist the force of combustion in said workingcylinders, said retaining means being removable so as to permit removalof said cylinder head, and said cylinder head being removable so as topermit removal of said front working piston from said cylinder borewithout removing said crankshaft from its position in said crankcase.

3. The combination recited in claim 1 including an inlet conduit boltedto the back end of Said cylinder structure for conducting inlet air tosaid engine, and said inlet conduit being also adapted to press againstthe end of said cylinder liner and thereby retain the cylinder liner inaxial position within said back working cylinder.

4. The combination recited in claim 1 'wherein said cylinder structureis provided with passages for Ithe flow of liquid coolant, and whereinsaid cylinder liner is of the 'wet type in which the liquid coolantllows directly against the outer surface of the liner.

15. The combinati-on recited in claim 4 wherein a seal ring of resilientmaterial is interposed between said liner and said cylinder structurefor the prevention of leakage of the liquid coolant, and wherein s-aidseal rin-g is located within an internal groove machined in the 4bore ofsaid cylinder structure.

i6. The combination recited in claim y1 wherein said front `workingcylinder is also .provid-ed with a cylinder liner and wherein said linerin the front working cylinder also serves to retain said cylinder headin axial position within said cylinder str-ucture.

7. The combination recited in claim 16 wherein the two cylinder linersare identical in size so as to facilitate interchangeability and reducethe number of dissimilar parts.

18. .In a double acting two str-oke cycle internal colmbustion engine, atirst -cylinder and a second cylinder, a lirst unitary pistonreciprocable in said Hirst cylinder, a second unitary piston.reciprocable in said second cylinder, said two cylinders being mountedin tandem, a cylinder head located `between said two cylinders, saidcylinder head having a bore smaller in diameter than either of saidcylinders, a reciprocable rod passing through said bore in the cylinderhead, said two unitary pistons being each fas-tened :to saidreciprooable r-od so as to reciprocate in unison, said cylinders each.enclosing a combustion chamber, one of said combustion chambers beinglocated on one side of said cylinder head and the lother combustionchamber being located on the other side of said cylinder head, each ofsaid unitary pistons having a hollow sleeve extending into said tbore inthe cylinder head, each of said hollow sleeves having a .ring groovemachined in its outer diameter, an expanding type seal ring mounted ineach of said ring grooves, said seal rings being adapted t-o ride insideand seal against said bore in the cylinder hea-d, said bore in thecylinder head being of sufficient length that said seal rings neverwithdraw from said bore during their reciprooative stroke, said sealrings serving to prevent the leakage of combustion gas trom each of saidcombustion chambers, and

said hollow sleeves serving to shield said reciprocable r rod from thellame and temperature in said combustion chambers.

y9. In a double acting two stroke cycle internal oombustion engine, thecombination of a crankcase, a crankshaft rotatably mounted in saidcrankcase, a cylinder structure fastened to said crankcase, saidcylinder structure having within it a front working cylinder and a backworking cylinder, .a cylinder head inserted into the -cylinderstr-ucture .and located between said front and back wonking cylinders,said front and back working cylinders having respective front and backcombustion chambers Within them, said back working cylinder havingwithin it a cylinder liner, a front working -piston recprocable in saidfront working cylinder, .a back working piston reciprocable in saidliner in the back working cylinder, said cylinder head having a centralbore, said pistons being mechanically interconnected through said borein the cylinder head so as to reciprocate in unison, a connecting rod:for converting the reciproca-ting motion of said pistons to the rotarymotion of said crankshaft, said liner having exhaust ports in its wall,lsaid exhaust ports being controlled by said back piston, said lineralso serving to retain said common cylinder head in axial positionwithin said cylinder struct-ure, said engine being adapted t-o be cooledwith liquid coolant, said cylinder structure :being provided Iwithpassages for 'the flow of said liquid lcoolant, said cylinder linerbeing of the wet type in which said liquid coolant flows directlyagainst the outer surface of the liner, said cylinder head having withinit a passage for the flow of liquid coolant, passage means forconducting the liquid coolant into said cylinder head, an ignition plughaving its ignition end titted into said cylinder head, said ignitionplug ibeing in -ring communication with said back combustion chamber,said ignition plug extending through .a hole in the wall of saidcylinder structure, a seal located around said ignition plug where theplug passes through said cylinder structure, and said seal serving toprevent leakage of said liquid coolant out of said cylinder structure.

10. In a double .acting two stroke cycle internal combustion engine, alrst cylinder .and a second cylinder, a -rst piston reciprocabl-e insaid rst cylinder, a second piston reciprocable in said second cylinder,said two cylinders being mounted in tandem, a cylinder head locatedbetween said two cylinders, said cylinder head havin-g a bore smaller indiameter .than either of said cylinders, a reciprocable rod passingthrough said bore in the cylinder head, said two pistons being eachfastened to said reciprocable rod so as to reciprocate in unison, saidcylinders each enclosing a combustion chamber, one of said combustionchambers being located on one side of said cylinder head and the othercombustion chamber being located .on the other side of said cylinderhead, each of said pistons having a hollow sleeve extending into saidbore in the cylinder head, :each of said hollow sleeves having -a .ringgroove machined in its outer diameter, an expanding .type seal ringmounted in each of said ring grooves, said seal rings being adap-ted toride inside and seal .against said bore in the cylinder head, said borein the .cylinder head being of suiiicient length that said seal ringsnever withdraw from said bore during their reciprocative stroke, saidseal rings serving to prevent the leakage of combustion gas `from eachof said combustion chambers to the other, said hollow sleeves serving toshield said reciprocable rod from the llame and temprature in .saidcombustion chambers, said pistons and said hollow sleeves being made ofmetal A, said reciprocable rod being made of metal B, metal A having ahigher thermal conductivity than meta-l B, metal A having a highercoefficient of thermal expansion than metal B, metal A having a lowerdensity than metal B, metal B having .a higher unit tensile strengthy(in terms of pounds per square inch of cross sectional area) than metalA, and the ends of the two said sleeves being separated by a gap so as.to allow for thermal expansion of the hollow sleeves relative to thereciprocable rod.

References Cited by the Examiner UNITED STATES PATENTS 874,634 12/07 St.Germain 12B-41.72 1,088,334 2/14l 'Edgar 92-151 1,149,5211A 8/15 Hunter123-4l.72 1,298,468 y3/19 Derihon 123-57 1,634,249 16/'27 Lindequist12B-57 1,900,133 3/36 Schaeers 12'3-57 2,154,249 4/49 Porter 123-59 FREDE, ENGELTHALER, Primary Examiner,

1. IN A DOUBLE ACTING TWO STROKE CYCLE INTERNAL COMBUSTION ENGINE, THECOMBINATION OF A CRANKCASE, A CYLINDER SHAFT ROTATABLY MOUNTED IN SAIDCRANKCASE, A CYLINDER STRUCTURE FASTENED TO SAID CRANKCASE, SAIDCYLINDER STRUCTURE HAVING WITHIN IT A FRONT WORKING CYLINDER AND A BACKWORKING CYLINDER, A CYLINDER HEAD INSERTED INTO THE CYLINDER STRUCTUREAND LOCATED BETWEEN SAID FRONT AND BACK WORK ING CYLINDERS, SAID FRONTAND BACK WORKING CYLINDERS HAVING RESPECTIVE FRONT AND BACK COMBUSTIONCHAMBERS WITH IN THEM, SAID BACK WORKING CYLINDER HAVING WITHIN IT ACYLINDER LINER, A FRONT WORKING PISTON RECIPROCABLE IN SAID FRONTWORKING CYLINDER, A BACK WORKING PISTON RECIPROCABLE IN A SAID LINER INTHE BACK WORKING CYLINDER, SAID CYLINDER HEAD HAVING A CENTRAL BORE,SAID PISTONS BEING MECHANICALLY INTERCONNECTED THROUGH SAID BORE IN THECYLINDER HEAD SO AS TO RECIPROCATE IN UNISON, A CONNECTING ROD FORCONVERTING THE RECIPROCATING MOTION OF SAID PISTONS TO THE ROTARY MOTIONOF SAID CRANKSHAFT, SAID LINER HAVING EXHAUST PORTS IN ITS WALLCONTROLLED BY SAID BACK PISTON, SAID LINER ALSO SERVING TO RETAIN SAIDCOMMON CYLINDER HEAD IN AXIAL POSITION WITHIN SAID CYLINDER STRUCTURE,SAID ENGINE BEING ADAPTED TO BE COOLED WITH A LIQUID COOLANT SAIDCYLINDER STRUCTURE AND SAID CYLINDER HEAD HAVING